How to build makeshift HDTV antennas from scrap parts. Credit for the bowtie type antenna design goes to the Solid Signal Blog. I don't claim to have invented these designs, but I see that there aren't many quick, makeshift antenna tutorials here on instructables, so I just thought I'd try to share their setups. Parts you may need:
1. 75 to 300 Ohm Matching Transformer ($1 to $3 on Amazon.) (It should adapt from twin lead to coaxial)
2. Two #6 or similar screws.
3. Small piece of wood board
4. Coax cable.
5. Two metal wire coat hangers.
6. If coat hangers are insulated, you will also need a wire stripping tool, if not, just use sandpaper to remove paint coating as needed.
7. If your are building the long-wire antenna design, you will need around 16 feet of enameled copper wire, which you can easily salvage from old stepper motors or transformers.
8. if you are building the simple loop antenna, you will also need a thick piece of copper wire because although coat hanger wire works fine for bowtie antennas, it is not optimal for any sort of loop antenna.

Step 1: Bowtie Antenna: 1. Cut the Coat Hanger Wire to Size

Cut hangers into two 20 inch pieces of wire and straighten out the wires as much as you can.

Step 2: Strip or Sand Hanger Wire.

If the wire you're using is insulated, use your wire cutter tool to strip a 1 inch section off the middle of each of the pieces of wire. If your coat hangers were just painted and not insulated, just sand a 1 inch section in the center of both pieces of wire so that the metal is exposed well.

Step 3: Fasten the Parts Together.

Bend each of the two pieces of wire like in the attached picture, and cut the wire so that each line is 8 inches long. then, use the screws to pin the two leads of the matching transformer to the wooden board so that the wire can conduct into the transformer/coax adapter. The distance between the two screws should be around 1 inch.

Step 4: Bonus 1: Simple Loop Antenna Design

Connect each end of a thick copper wire to form a 7.5 inch diameter ring (this diameter is found by calculating as the middle in the range of wavelengths of the frequencies which correlate to the channels I want to pick up in my area), fasten the ends by bending hooks onto the leads or connectors on the balun (matching transformer) and your done making the simple loop antenna!

Step 5: Bonus 2: Folded Dipole Antenna Design

Cut the coat hanger around where the original hook was, and sand off the insulation near the ends... Fold hooks onto the wire ends and fasten those onto your matching transformer balun by the screws or just by clamping onto the leads depending on which type of balun/transformer you have. All done!

Step 6: Bonus 3: Long-Wire-Loop Antenna Design

Sand the ends of the roughly 16 foot long enameled wire to expose the copper. Then hang the length of wire over a balcony like I did, or perhaps run the wire under a window will to outside on the roof (not too high up, don't attract lightning!)... fasten the ends of the wire to the matching transformer with screws or by wrapping around the leads. make sure the wire loop isn't twisted around itself, so as not to lessen the signal. All done!

Step 7: Connect to TV and Scan for Channels

connect the coax adapter end of the antenna to the coaxial cable going to your TV. You may need a male to male coaxial adapter. If your TV is not a digital ready HDTV, (most TVs are) then you may need to go through a Digital TV Converter Box. Then, navigate to the tuner page in your TV's settings, and select scan for channels (usually the cable or antenna input options) I was able to pick up 35 different DTV channels from indoors!